Dear Nucking Futs,
You have fallen to the old magicians trick. You have been focused on the left hand and did not see what the right hand was doing.
The intake is no longer the problem, but you were zeroed in on it like a hawk on a mouse.
Are the two valve covers identical in the milk shake? If one is worse, I suspect that head is leaking up into the valve cover area. If they are identical, I would suspect that a head gasket is leaking into the
oil area some where. Is there any indication (milk shake) in the lifter gallery.
Also be careful with the nitrogen. One lung full and your dead.